Over the last fifty years, approaches toward providing animal nutrition have changed. No longer are the animals fed whatever grain or forage may be available. Instead, the diets of animals are closely monitored for total nutrition value, and for cost. The animal on the diet is monitored, for quality and performance characteristics, and for the environmental impact of the waste from the animal. The information gathered is employed to adjust the feed to increase nutrition value of the feed and the animal performance characteristics while decreasing the cost and environmental impact.
Cereals account for about half of all feed ingredients, primarily because they are good sources of energy. Maize tends to be the preferred feed grain because of its highly digestible carbohydrate and relatively low fiber content, which is particularly important for swine and poultry (Hard, Proc. Southwest Nutr. Conf. 43-54 (2005)). Because of the low protein content of maize, it is common practice to use feed additives and supplements, such as protein-rich feeds, amino acids, vitamins, minerals and fats in diets for swine and poultry. The ratio of cereals to supplements has changed through the years in an attempt to maximize feeding efficiency of the animals. The feeding efficiency (the feed conversion ratio or how much feed is required to produce one pound of animal weight) is determined by the genetic potential of the animal and by the nutrients supplied to the animal. As the feed conversion ratio has risen due to genetic enhancements, the mineral and nutrient requirements for feed necessary to assure a complete and healthy diet have risen. Since an animal's ability to feed limits the amount of nutrients and calories it can consume, the feed industry has had to develop ways to make feeds that have improved protein quality (improved balance of essential amino acids), digestibility (fiber, starch, anti-nutrients), and metabolizable energy (oil).
Sources of feed protein have come under global public scrutiny in recent years because of the bovine spongiform encephalopathy, or mad cow disease, crisis associated with the feeding of meat and bone meal as the primary protein source in animal diets in many parts of the world. Plant protein sources, especially soybean meal, a residual product of the oil extraction process from soybeans relatively high in protein, have become a dominant alternative protein supplement used in feed following bans on using meat and bone meal in many parts of the world.
Plant protein sources, however, may lack sufficient levels of essential amino acids required for adequate animal health, growth and performance. Requirements vary depending on the species and age of the animal. For example, the order of the top three limiting amino acids in feed composed of corn and soybean meal is lysine, threonine, and tryptophan for swine and methionine, lysine, and threonine for poultry. (FAO Animal Production and Health Proceedings, Protein Sources for the Animal Feed Industry, xi-xxv, 161-183 (2004)). These limiting amino acids must be available at specific minimum levels in order for the animals to use dietary protein efficiently. (Johnson et al. “Identification of Valuable Corn Quality Traits for Livestock Feed”, Report from the Center for Crops Utilization Research, Iowa State University, 1-22 (1999)). Crude protein in feed ingredients is not totally digestible for any species, for example corn protein is approximately 84% digestible by poultry and 82% digestible by swine (Johnson et al. (1999)). To compensate for this inefficiency, feed often contains excess protein that then results in high nitrogen excretion. More stringent environmental regulations are being imposed because high nitrogen excretion poses serious concerns to human health through ammonia or nitrate/nitrite pollution in soil and water. One solution to the problems of nitrogen pollution associated with animal feeding is to decrease crude protein in feed and supplementing feed with amino acids. A one-percentage point reduction in crude protein content in feed can yield about eight to ten percent reduction in nitrogen excretion. (FAO Animal Production and Health Proceedings, Protein Sources for the Animal Feed Industry, 161-183 (2004)). Supplementing of feed with amino acids can provide the required nutrients while decreasing excessive crude protein and can provide limiting amino acids when they are not sufficiently available.
Additionally, animals lack the enzymes necessary to digest the non-starch based polysaccharides present in soybean meal, and corn/soybean feed mixtures resulting in high manure volume and environmental impact. Approximately 65 to 70% of the total phosphorous in cereal grains is organically bound in phytate phosphorous, which is relatively unavailable to poultry and swine because they lack the enzyme phytase required to digest phytate, thus requiring inorganic phosphorous supplements. (Knowlton, J. Anim. Sci. 82(E. Suppl.):E173-E195(2004)). The undigested phytate passes through the digestive system and leads to excretion of excess nutrients resulting in high manure volume and high levels of phosphorus in manure. Manure containing nitrogen and phosphorous at levels in excess of crop requirements results in environmental contamination especially of water resources caused by runoff. Enzymes, such as phytase, are commonly added to feed to increase digestibility. The addition of phytase can reduce the level of phosphorus released in animal waste to about half the previous level. However, the cost of phytase is about three times the cost of the conventional inorganic phosphorous supplements usually added to feed. (“Enhanced Animal Feed Will Be A Boon For The Environment,” Economic Perspectives, Agricultural Biotechnology, An Electronic Journal of the U.S. Dept. of State, Vol. 8, No. 3, September 2003).
End-users of feed corn include livestock producer-feeders, feed manufacturers, corn millers and processors. Whether for a livestock producer-feeder who mixes and prepares their own feed or for a feed manufacturer who supplies a variety of feed products including complete ration feeds or nutrient supplements, each of the various ingredients necessary to produce the right combination of nutrients (i.e. protein, amino acids, enzymes, etc.) will need to be transported from site of production and/or processing to the site of the end-user. The availability, price, and transportation requirements and costs of each component of a particular feed will vary from year to year and in different geographical regions. Feed is usually formulated to meet nutritional requirements at a minimum dietary cost. The feed industry balances rations to supply nutrients at the least cost. Because of the variability of the supply and cost of nutrients and additives, livestock feeders and feed manufacturers would value corn traits that create substitutability for more expensive feedstuffs or additives.
Because feed is around 60% of animal production costs, any savings can be considerable, especially in large operations. Nutritionally enhanced corn which can deliver higher levels of important nutrients and metabolizable energy, and/or enhanced digestibility and bioavailability of nutrients would provide the following benefits: reduced feed costs per unit weight gain or production of eggs or milk; reduced animal waste, particularly nitrogen and phosphorous; reduced veterinary costs and improved disease resistance; improved processing characteristics to make the feed; and improved quality (Johnson, et al. (1999)). Cost savings can be achieved by using nutritionally enhanced corn through, for example, reduced cost for needed supplements and synthetic additives, reduced transportation costs associated with the shipping of each additive and ingredients to produce the additives, reduced cost in mixing numerous additives during feed processing, and reduced costs associated with disposal of excess volume of manure.
Both traditional plant breeding and biotechnology techniques have been used to develop maize plants with desired traits such as low-phytate, high-lysine, or high-oil maize. For example, U.S. Pat. No. 5,723,730 describes an inbred corn line used to produce a hybrid with elevated percent oil and protein grain.
Examples of grain-based feed that provide improved animal nutrition and can reduce environmental impact of animal production are described by Chang et al. in U.S. Pat. Nos. 7,087,261 and 6,774,288 and in U.S. Publ. No. 2005/0246791.
There remains a need to develop inbred parental maize lines that contribute these desirable traits to the hybrids in which they are used. These traits may also include resistance to diseases and insects, tolerance to heat and drought, reducing the time to crop maturity, greater yield, and better agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination and stand establishment, growth rate, stalk strength, root strength, ear retention, maturity and plant and ear height, are important. Selection of germplasm that possess the desired traits is required to develop novel, desirable plant germplasm for plant breeding.
Maize is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding maize hybrids that are agronomically sound. The reasons for this goal are obviously to maximize the amount of grain produced on the land used and to supply food for both animals and humans. To accomplish this goal, the corn breeder must select and develop maize plants that have the traits that result in superior parental lines for producing hybrids and that provide end-user value.